"Your mission is for us a last-chance mission because seven others have come before you," Ouattara told the four African presidents as the impasse dragged towards its fourth month amid rising tensions and fears of civil war.

The presidents, dispatched by the African Union as Gbagbo defies pressure to step down after losing November 28 elections, presented Ouattara with proposals to end the dispute.

The South Africa government, whose President Jacob Zuma is on the mediation team, said they centred on forming a power-sharing interim government to run the country until new polls are held.

The latest mediation bid comes amid rising tensions in Abidjan after deadly clashes between the two camps since the weekend, with Ouattara's camp calling for a "revolution" like the uprisings in Tunisia and in Egypt.

At the meeting Ouattara accused Gbagbo's men having "violently suppressed" demonstrations by his followers on Monday, saying 12 were killed, some of them in fire from rocket-launchers, an AFP reporter said.

Newspapers reported that at least six people were killed in the clashes in Abidjan.

The mediators hoped for an outcome which "beyond the Ivory Coast is going to save peace in the sub-region, in all of Africa," said Mauritanian President Mohamed Ould Abdel Aziz, leader of the mission.

"We are not at the end of our efforts," he admitted at the talks at an Abidjan hotel where Ouattara is under a blockade by Gbagbo's forces.

The mediation team, which also includes President Idriss Deby Itno of Chad and Jikaya Kikwete of Tanzania, met Gbagbo on Monday. The African Union wants them to find a binding solution to the standoff by February 28.

"They're trying to find some type of compromise solution whether they should share the presidency between the two presidents and whether they should continue with the interim government until they have new elections," South Africa's Deputy Foreign Minister Ebrahim Ebrahim said.

Ouattara's supporters heckled South Africa's president at the end of the meeting, calling him a "thief" and shouting "Zuma tell the truth". They claim he is an ally of Gbagbo.

An aide for Ouattara said he was unhappy with the absence in the delegation of President Blaise Compaore of Burkina Faso, who cancelled his visit after threats from loyalists of Gbagbo accusing him of being an ally of Ouattara.

The Economic Community of West African States (ECOWAS), which has adopted a tougher line than the African Union and threatened the use of force to oust Gbagbo, also slammed the mediation effort for going ahead without Compaore.

The "threat was serious enough to compel the facilitator (Compaore) to cancel his planned participation in the trip to Abidjan," it said in a statement.

The "panel nevertheless took the decision to go ahead immediately with the visit without the participation of an important member," it said.

Compaore's "invaluable contribution" to the process "deserves better appreciation and respect," it said.

Witnesses said that for several hours Monday Abidjan's working-class neighbourhoods of Abobo, Koumassi and Treichville were urban warfare zones with clashes between supporters of Ouattara and the Gbagbo-allied Forces of Defence and Security.

Gunfire rang through the streets and roads were barricaded with tables and burning tyres, they said.

Post-electoral violence has claimed at least 300 lives since mid-December, according to the United Nations.